1. Technical Field
The present invention relates to automatic focus tracking systems and more particularly, to an automatic focus tracking system for use with a gas platform.
2. Description of Related Art
Precision inspection is usually applied to products which require high precision and low fault tolerance rate, performed in conjunction with an automated production line, and located at the end of a supply chain, so as to inspect the surfaces of finished products for defects, such as smears, abrasions and copper exposure. Precision inspection is usually carried out with an optical instrument, such as a line-scan camera or an area-scan camera, to capture images of the surface of a workpiece, and then defects, such as foreign bodies or pattern abnormalities, are identified by computer-based image processing technology.
An inspection process performed on precise workpieces, such as panels, entails conveying the workpieces with a conveyor belt. The workpieces must be prevented from being scratched or smeared by the conveyor belt and thus incurring defects. To this end, a gas platform is provided to carry some of the precise workpieces so that the workpieces are subjected to a positive pressure under which the workpieces are suspended and thereby prevented from coming into contact with a plane below. The workpieces being conveyed need to be inspected, even though the workpieces are suspended above the gas platform under a positive pressure provided by the gas platform, with a suspension height clearance of 300 um or so. However, conventional cameras have a depth of field of just 35 um and thus cannot capture images of an object not within the depth of field. In view of this, the gas platform inevitably requires a quick efficient focus tracking technique.